1. Field of the Invention
Piston cooling spray nozzles for internal combustion engines are used to spray a cooling fluid such as oil onto the back of the piston, i.e. onto the face of the piston outside the combustion chamber, or into a piston tunnel.
2. Description of the Prior Art
The piston cooling spray nozzles usually employed are separate parts fixed to the engine block and communicating with a cooling fluid feed orifice. The position of the spray nozzle must be precisely determined to determine precisely the point of impact of the jet of cooling fluid on the back of the piston or in the piston tunnel.
One technique known in itself, described for example in document DE-A-19 57 499, consists in providing a one-piece spray nozzle body limited by a bearing face and by an opposite fixing face, provided with an axial bore through which a fixing and fluid feed screw-valve extend. The axial bore communicates with a transverse bore connected to a cooling fluid outlet injection conduit. The screw-valve is shaped and adapted to hold the spray nozzle body with its bearing face pressed against the peripheral area of a fluid feed orifice in the engine block wall and to transmit the cooling fluid to the inlet of the transverse bore. The screw-valve screws into a screwthreaded end portion of a cooling passage discharging through the fluid feed orifice. Centering and rotation preventing means are used to position the spray nozzle body in the engine cylinder. In the above document, these centering and immobilizing means comprise a ball engaged in corresponding housings in the engine block and the spray nozzle body.
A one-piece cooling spray nozzle body of this kind is made of metal and can be machined from a block of metal or cast and machined. In all cases, it is a part of complex shape and therefore has a high production cost. Moreover, the necessary clearance between the screw-valve and the screwthreaded bore in the engine block which receives it introduces uncertainty as to the final position of the spray nozzle and the position at which the jet of cooling fluid impacts on the back of the piston. Furthermore, the centering and rotation preventing means significantly increase the volume and the manufacturing cost of the spray nozzle.
Furthermore, defective seals have been found between the spray nozzle body and the engine block wall with the result that some of the cooling fluid escapes directly between the spray nozzle body and the engine block wall and does not reach the piston
Other complex shapes of one-piece spray nozzle body are described in the documents U.S. Pat. No. 2,991,769 and U.S. Pat. No. 4,010,718.
Document DE-A-34 16 076 discloses a piston cooling spray nozzle in which the spray nozzle body is held by a fixing plate fixed by screws passing through two holes in the plate. The fixing plate has a central excrescence penetrating to the interior of the spray nozzle body. This mode of fixing is very different from a screw-valve and necessitates additional machining in the engine block wall.
The problem addressed by the present invention is that of designing a new screw-valve type spray nozzle structure for piston cooling that can be manufactured at significantly less cost than the structures known in themselves, that provides all the centering and rotation preventing functions required for precise positioning of the spray nozzle in the engine cylinder, and which enhances the orientation precision and reproducibility with which the jet of cooling fluid is sprayed onto the back of the piston.
The present invention is the result of the observation that the piston cooling spray nozzle body has a complex shape adapted to provide multiple functions: some shape parts are designed to center and prevent rotation of the spray nozzle body in the engine cylinder; other shape parts are designed to conduct the cooling fluid and to provide a seal between the spray nozzle body and the engine block wall as well as forming and directing the jet of cooling fluid. The idea is to have the parts of the spray nozzle assuring the fluid conduction and sealing functions also assure the centering and rotation prevention functions.